Method of grinding metal powder



United States Patent US. Cl. 24116 8 Claims ABSTRACT OF THE DISCLOSURE Finely divided metal powders, surface area greater than 2 square metres per gram, can be formed by grinding metals in an Organic liquid containing a load-carrying additive. The load carrying additives are phosphorous and/or chlorine and/or sulphur containing substances.

This invention relates to improvements in metal powders. In particular this invention relates to metal powders with a high surface area.

Finely divided metal powders have been used for the fabrication of metal articles (by sintering of the powders), as pigments, as fillers for plastics, as reagents, as rocket propellants, as solders and brazes etc.

Although it is known to produce metal powders by chemical techniques such as vapour condensation or precipitation from solution, it is recognized that mechanical grinding provides, in general, a cheaper route for obtaining these powders. Among known grinding methods are the use of planetary ball mills, attritor ball mills and vibratory ball mills.

It has also been known for some time to carry out the grinding of metals in a grinding fluid, for example, a petroleum fraction, ethanol, methylene dichloride, or nheptane etc. Furthermore the use of grinding aids, such as the fatty acids and their metal salts, for example, stearic acid and aluminium stearate, is known. A useful source of information on this subject is Ultrafine Particles, edited by W. E. Kuhn, published by Wiley in 1963. It has been suggested that the function of a grinding aid is to prevent agglomeration of the ground particles during the grinding.

However, metal powders produced by prior art methods have the disadvantages of low surface areas and little lubricating activity.

It is an object of the present invention to provide finely divided metal powders with a high surface area and a high reactivity and which act as solid lubricants.

According to the present invention a finely divided powder is prepared by grinding a metal in the presence of an organic grinding fluid and an organic load-carrying additive containing one or more of the elements sulphur, chlorine, phosphorus and nitrogen.

Suitable organic grinding fluids are those liquids which distil below 500 C. have a viscosity below 600 centistokes at 100 F. and have a viscosity of below 72 dynes/cm. at 25 C. and preferably have a viscosity of 10 to 40 dynes/cm. at C. In a preferred embodiment of the invention the grinding fluid is a hydrocarbon, especially for example, n-heptane, iso-octane, cyclohexane, toluene, hexadecane or a hydrocarbon fraction obtained by the distillation of petroleum.

Organic load-carrying additives are very well known and are extensively used in lubricating compositions.

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Their function is to improve the anti-wear properties and/ or the extreme pressure properties of the lubricating compositions. When two lubricated moving surfaces are lightly loaded against each other, they are separated by an elasto-hydrodynamic oil film; as the load increases so the oil film thickness decreases. When the oil firm thickness approaches the dimensions of the surface roughness, it will be penetrated by surface asperities; it is in this region that antiwear additives function by improving the oil film strength and thus reducing intermetallic contact. As the load is increased further, the bulk oil film collapses and antiwear additives are no longer suflicient to protect the surface. Extreme pressure additives function in this region by reacting With the metal surfaces to form an inorganic iron compound which prevents the welding of the metal surfaces.

The term load-carrying additives includes both antiwear and extreme pressure additives.

The load-carrying additives which can be used in the present invention are those which contain one or more of the following elements: chlorine, sulphur, phosphorus and nitrogen.

Examples of suitable load-carrying additives are organic chlorine-containing compounds such as the lowmolecular weight chlorinated hydrocarbons, preferably those containing from 1-4 carbon atoms e.g. carbon tetrachloride; chlorbenzyl esters of alkyl xanthic acids and of thioacids such as thiocarbonic acid; and chlorinated hydrocarbon waxes.

Other suitable load-carrying additives are the covalent sulphur-containing compounds such as the di-phenol polysulphides, e.g. di-(4-hydroxy phenol) polysulphide; alkyl and aryl thioethers; alkyl and aryl thiocarbonates and thiocarbamates; sulphur substituted carboxylic acid esters e.g. acetic esters substituted in the a-position by sulphur; sulphurised polymers, e.g. sulphurised butadiene- 1,3/styrene copolymer; the reaction product of sulphur and polyalkylene glycols; alkyl disulphides e.g. di-n-butyl disulphide and di-(Z-ethyl hexyl) disulphide; and di-aryl disulphides e.g. di-benzyl disulphide and di-(amino benzyl) disulphide.

Further suitable load-carrying additives are the phosphosulphurized organic compounds typical organic materials which can be phosphosulphurized include oxygen containing waxes; chlorinated phenols; waxy esters; cyclic ketones; hydrogenated sperm oil; esters of unsaturated acids, e.g. glycol and glyceryl oleates; and abietic esters.

Yet further suitable load-carrying additives are organic compounds containing phosphate or thiophosphate groups such as tri-aromatic phosphates e.g. tri-cresyl phosphate; trialkyl phosphates such as tributyl phosphate; and metal dialkyl dithiophosphates such as the zinc dialkyl dithiophosphates.

Organo metallic compounds such as organo-tin dithiophosphates and lead naphthenate can be also used as load-carrying additives.

Compounds containing nitrogen which can be used include phosphoramidates, for example those described in UK. Patent 899,101; nitrobenzenes; nitronaphthalenes; amine phosphates; tetra alkyl ammonium phosphates and thiophosphates; and rhodanine and rhodanine derivatives.

Any compound which aids the load-carrying properties of a lubricating composition can be used in the present invention.

3 When the organic grinding fluid is also a load-carrying additive e.g. carbon tetrachloride, then no other loadcarrying additive need be added.

Any metal or alloy which can be ground can be used in the present invention, the preferred metals being iron,

It has also been unexpectedly found that the finely divided metal powders of the invention can be used as grease thickeners. In order to produce a grease the finely divided metal can simply be stirred into a base oil, or, alternatively any of the methods of grease formation deincluding mild steel and cast iron, and aluminium. Other scribed in UK. application 40,701/65 can be used. suitable metals are the transition metals, for example, The following example serves to illustrate the invennickel, cobalt, chromium and titanium, copper, and coption. per alloys such as brass. EXAMPLE In a preferred embodiment of the invention a high Iron powder was ground in a Megapact Mark speed, vibratory ball mlll is used. The grinding balls are vibratory ban min (manufactured y Pnamec Limited) preferably made of hardened steel. for three hours The grmdmg 18 preferably earned out the metal In this mill the grinding chambers are steel cylinders powder produced has a Surface area f at 2 of 1 /2 inch internal diameter by inches long and are g z i ,fg g j fg a bu k denslty 15 nearly filled with inch diameter hardened steel balls. 5 a Own 0 655 an The mill is fitted with a one eighth horsepower electric It 15 thought that the load'carrymg .lddmves are l motor and the oscillation can be adjusted from 1 to 4 Sorbed on the slllrface i 2 3 i ggigg igi g g mm. In operation, each cylinder was filled completely some cases ayerlo g e F 9 with n-heptane, containing dissolved therein a load-carryformed on t e meta ace unng gm} or exing additive and the steel balls and from 10 to grams ample, carbon tetrachloride may react with the surface of iron povzlder from to 400 British Standard mesh of pamcles of finely ground Iron gwmg Iron chlorides were added This first about from 150 to 250 cc n-heptane etc I in each cylinder. The ends were then sealed with metal In general terms i bate}: the load carrymg i l caps fitted with rubber washers and the grinding carried ties of the load carrying additive, the more effective it 1s 25 out. After grinding the balls were sieved from the slurry Pf' the finely dlvldFd metgpowders of the of iron powder and n-heptane and load-carrying additive VentlOfl- However loadcan'ymgfiddliwes can have Vary and the treated iron powder recovered by filtration, washing effectiveness when used with different metals, and i and drying it is desirable that the load-carrying additive is selected 30 The surface, areas and bulk densities obtained using with reference to the metal to be ground. various additives are given in Table I below:

TABLE I 01 found Amount of Siound in B.E.T. Bulk additive in in powder surface density percent powder, in area after wt., percent percent of iron shake Load-carrying additive in n-heptane/ Wt. wt. powder down, n-heptane additive powder powder in mfl/g. g./cc.

Experiment No.1

1 2 1.35 2.... Carbon tetrachloride 0. 5 3.-.. .do 1.0 4 -do 2.0 5.. Dibenzyl disulphide 0. 5 6-- ..d0.. 1.0 7 2.0 a. 0.5 9-. 1.0 10 do 2.0 11..- Phosphosulphurized terpene 0. 5 12 do 1.0 13..- .do 2.0 14 N -lauryl phosphoramidate 0.5 15 Zinc dithiophosphate 0.5

l The bulk density was measured by placing some of the finely divided metal in a measuring cylinder shaking the powder down till the measured volume was constant, and then weighing the amount of powder.

It can be seen from this table that carbon tetrachloride gives the greatest surface area upon grinding iron powder according to the invention. It appears furthermore that certain concentrations of load-carrying additives provide optimum increases in surface area.

Nickel, molybdenum and chromium powders were also ground in n-heptane in the presence of carbon tetrachloride and the results are shown in Table II.

TABLE II Amount of B.E.T. Bulk additive in surface density Percent wt. area of after Load-carrying n-heptane/ powder shake Metal additive in n-heptane additive in mfl/g. down (5) Cr- (6) Unground Ni (7) Unground Cr Nora-A11 the grinding fluid was carbon tetrachloride.

The load-carrying activity of the powders was measured using dispersions of the powders in a base oil tested in a Four Ball Tester. The results are tabulated in Table III below:

6 from copper, aluminium, iron, cobalt, nickel, molybdenum and alloys thereof.

5. A method of preparing a finely divided metal powder which comprises grinding the metal in an organic grind- TABLE III Amount of solid in oil, Wear as measured Percent by wear scar diameter; Base oil Solid dispersed in oil wt Lead 115 kg., 30 min.

(1) Medicinal parafiin oil Welds in less than 1 min. (2) Medicinal paraflin oil Oleophilic graphite 5 4.0 mm. in 1 min. (3) Medicinal paraflin oil Oleophilic M08 5 0.99 mm. in 30 min. (4) Medicinal parafiin oil Iron powder ground in n-heptane, no additive- Welds in less than 1 min. (5) Medicinal parafiin oil- Iron N0. 2..-. 10 1.08 mm. in 30 min. (6) Medicinal paraffin oil- Iron N 0. 11 10 2.21 mm. in 30 min.

1 See co-pending application No. 40,702/65. 1 See co-pending application No. 40,700/65.

It can be seen from this table that the load-carrying properties of the treated iron are equivalent to those of oleophilic molybdenum disulphide, which substance has excellent extreme pressure activity.

The load-carrying activity of an iron powder prepared according to the invention and disposed in a B6 160/95 base oil was tested in a' Four Ball Tester. This base oil has a Redwood I viscosity at 140 F. of 160 seconds and a viscosity index of 95. The results are tabulated in Table IV below:

TABLE IV Wear Scar Wear Scar Amount Diameter: Diameter:

of solid Load Load in oil, 15 kg., 115 kg., Mean Solid disposed Percen 60 min., min., Hertz Base oil in oil wt. mm. mm. Load (1) B G 160/95 0.80 2. 64 22. 6 (2) BG 160/95 Iron No. 2---- 5 0. 76 1. 5 28. 7

I claim: N-lauryl alkyl phosphoramidate, and chlorinated paIafiins 1. A method of preparing a finely divided metal powder which comprises grinding the metal in an organic fluid distilling below 500 C. in the presence of an organic load stokes at 100 F., and of surface tension less than 72 dynes/cm. at 25 C. in the presence of an organic load carrying additive for lubricants containing at least one element selected from sulphur, chlorine, phosphorus and nitrogen.

2. A method as claimed in claim 1 in which the said organic grinding fluid is n-heptane, iso-octane, cyclohexane, toluene, hexadecane or a hydrocarbon fraction obtained by distilling petroleum.

3. A method of preparing a finely divided metal powder which comprises grinding the metal in an organic grinding fluid in the presence of an organic load-carrying additive for lubricants selected from the group consisting of phosphosulphurised terpenes, zinc dialkyl dithiophosphates, di-aryl disulphides, di-alkyl disulphides, N-lauryl alkyl phosphoramidate and chlorinated parafiins containing from 1 through 4 carbon atoms.

4. A method of preparing a finely divided metal powder as claimed in claim 3 in which the said metal is selected containing from 1 through 4 carbon atoms.

7. A method of preparing a finely divided iron powder which comprises grinding iron in a parafiinic hydrocarbon distilling below 500 C., of viscosity less than 600 centistokes at F. and of surface tension less than 72 dynes/ cm. at 25 C. in a vibration ball mill in the presence of carbon tetrachloride till the iron powder has surface area of at least 5 square metres per gram and a bulk density of less than 1 gram per cc.

8. A method of preparing a finely divided metal powder as claimed in claim 5 in which the said load-carrying additive is present in an amount of up to about the weight of the metal.

References Cited UNITED STATES PATENTS 1,569,484 1/1926 Hall 241-46 X 2,976,239 3/1961 Sabol 252-32.7 3,070,546 12/1962 Butler 25232.7 3,252,842 5/1966 Williams 24116 X ANDREW R. JUHASZ, Primary Examiner (2);? UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,476,325 Dated November 4, 1969 Inventor) Aleksander Jerzy Groszek It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, between lines 6 and 7 insert --Claims priority,

application Great Britain, Aug. 5, 1966, 351l9/66-- Colman 4, Table 11 Item 3 "100" should read --1oo Column 4, bottom line, "NOTE.A11" should read A1l--;

Column 5, lines 44-45, "in the presence of an organic load stokes at 100F.," should read of viscosity less than 60 centistokes at l00F.,--.

SIGNED AND SEALED JUN161970 (SEAL) Attest:

Edward M. Fletch, Jr- WIL'LIMI E. 501mm, J8

LAm fi ()ffi Gomissioner of Patent: 

